Hot-gas engine heater

ABSTRACT

A hot-gas engine in which the heater is formed by a number of pipes which are arranged in the flow path of a combustion gas flow and which are arranged over a part of their length inside a common heat pipe which is elsewhere provided with a heat source so as to equalize the temperature of the pipes.

I United States Patent 1191 1111 3,863,452

Asselman et al. 1 Feb. 4, 1975 [54] HOT-GAS ENGINE HEATER 3,029,596 4/1962 Hanold et al. 60/524 [75] In ento s G g lbert Apolonia Asselman; 3,702,533 11/1972 Dlrne et a1 60/524 Reimnk; 1059p Wilhelm FORE1GN PATENTS OR APPLICATIONS Johannes Maria Der Leegte 630 428 /1949 Great Britain 60/524 2 212112 Emdhoven 2,015I202 10/1970 Germany ......1..:.IIIIIIIII:: 60/524 [73] Asslgnee: x g Corporation Nfiw Primary Examiner-Martin P. Schwadron or Assistant Examiner-H. Burks, Sr. [22] Filed: Aug. 15, 1973 Attorney, Agent, or FirmFrank R. Trifari; J. David 211 App1.No.:388,60l Damow Foreign Application Priority Data [57] ABSTRACT Sept. 22, 1972 Netherlands 7212824 A g engine in which the heater is formed y a number of pipes which are arranged in the flow path of a Combustion gas flow and which are arranged over I a part Oftheir length inside a Common heat pipe which [58] Fleld of Search 60/517, 524, /105 is elsewhere provided with a heat Source so as to References Cited equalize the temperature of the pipes.

UNITED STATES PATENTS 5 Claims, 2 Drawing Figures 2,596,057 5/1962 Van Heeckeren et a1 60/524 PATENTED FEB 41925 sum 1 or '2 HOT-GAS ENGINE HEATER BACKGROUND OF THE INVENTION The invention relates to a hot-gas engine having at least one working space, space of variable volume and lower mean temperature and an expansion space of variable volume and higher mean temperature which communicates therewith, via a cooler, a regenerator and a heater. The heater is formed by a number of pipes which are arranged in the flow path of hot combustion gases originating from a common burner device.

A hot-gas engine of this kind is known as appears from British Pat. Nos. 708,199 and 898,270. The heater is a heat exchanger in which thermal energy is given off to working medium in the engine. To this end, the combustion gases flow along the heater pipes while giving off heat to the working medium flowing through the pipes.

It was found that the temperatures of the working medium in the various heater pipe bundles can differ substantially, particularly in multi-cylinder hot-gas engines having one central burning device as known from British Pat. No. 708,199. This may have various causes: for example, a deviation in the burning position of the burner can cause one bundle of heater pipes to receive more heat than the other; furthermore, temperature differences can be caused, in that unequal flow losses and leakage losses of the working medium occur for the different cylinders. Not only the flow resistances of the pipe bundles associated with the individual cylinders can then differ, but the flow resistance of the individual pipes associated with a cylinder can also differ. The observed temperature differences exert an adverse effect on the power and the thermal efficiency of the engine. The invention has for its object to provide a hot-gas engine in which the said drawbacks are simply eliminated.

SUMMARY OF THE INVENTION The hot-gas engine according to the invention is characterized in that the heater pipes are arranged over a part of their length within a common heat pipe which is elsewhere provided with a heat source for maintaining the same temperature to the relevant heater pipe parts during operation of the engine.

In the context of the present description, a heat pipe is to be understood to mean a heat transport device which is formed by a reservoir in which a small quantity of a heat transport medium, for example, sodium, is present which evaporates on one side from a reservoir wall by taking up heat from a heat source, and which on the other side gives off heat to another reservoir wall while changing from the vapour phase to the liquid phase.

By a heat pipe large quantities of heat can be transported substantially without the occurrence of a temperature drop and without the use of a pumping device or other moving parts being required. Heat transport medium condensate can be returned to the wall where evaporation takes place by gravity. However, the heat pipe often contains a capillary structure which connects the condensation wall to the evaporation wall, and through which condensate is returned to the evaporation wall under all circumstances by capillary action. Heat pipes which are provided with a capillary structure for the return of condensate are known, for example, from US. Pat. Nos. 3,299,759 and 3,402,767.

In the present case, the major advantage of the use of the heat pipe is based on the fact that most of the heat transport medium vapour in the heat pipe always condenses on the heater pipe parts which have the lowest temperature, i.e., the heater pipe parts in which most heat is taken up from the pipe walls by working medium of the engine. Consequently, and due to the absence of temperature gradients over the thermal connections between the heat source and the heater pipe parts, it is achieved that the heater pipe parts themselves are isothermal and all have the same temperature. As a result, the working medium flowing through the various heater pipes (bundles), assumes the same temperature everywhere.

From a construction point of view, the heat pipe can be readily added on already existing engines having direct heating by combustion gases, while a large degree of freedom remains as regards the location where the heat pipe is mounted on the heater pipes. Furthermore. the thermal load of the heat pipe is particularly low.

It is to be noted that Swiss Pat. No. 512,670 (corresponding to German Pat. No. 2,015,202) describes a hot-gas engine which is heated by combustion gases and in which the heater pipes are accommodated over a part of their length in a vessel which is filled with a heat-accummulating material. A heat buffer of this kind is unsuitable for various reasons for use as a temperature equalizer for the heater pipe parts situated therein.

The heat buffer, considering its heat transport by conduction, has a heat resistance which is thousands of times higher than that of the heat pipe. Consequently, permanently colder areas arise in the heat buffer when heat is withdrawn from the heat buffer by the working medium in these heater pipes. As the working medium in a pipe withdraws more heat, a locally lower temperature appears. The lower temperatures are insufficiently compensated for due to the insufficient heat flows from the heat-accumulating material. If the vessel contains liquid heat-accumulating material, for example, this material will solidify at the area of the heater pipe parts of lower temperature, and the thermal resistance in the heat buffer increases substantially.

in the hot-gas engine according to the invention the heat pipe performs its temperature-equalizing function substantially from the instant at which the engine is started, but in the hot-gas engine described in said Swiss patent, the heat buffer actually constitutes an element which hampers the equalization of the working medium temperature in the various heater pipes for a substantial period after the engine has been started. Due to the comparatively high heat capacity and the poor heat conduction of the heat buffer material, a substantial period of time is required for heating this material to the operating temperature. Particularly because of the poor heat conduction, substantially no heat exchange occurs during this period between the heater pipe parts themselves, so no temperature equalization occurs either.

An auxiliary burner or an electric heating element, inside or outside the heat pipe, can be used as a heat source for the common heat pipe. According to the invention, the common heat pipe comprises a heattransmitting wall which is arranged in the flow path of the combustion gases and which is in thermal contact with a part of the combustion gases. As a result, further aids are unnecessary and the heat pipe requires no special structural provisions.

In a preferred embodiment of the hot-gas engine according to the invention, the construction of the heat source is such that it maintains the heater pipe parts at a temperature which is at least substantially equal to the mean temperature of the heater pipe parts outside the heat pipe which are directly heated by the combustion gases. The heat pipe then equalizes the temperature to a value which is substantially equal to the desired working medium temperature in the heater pipes. The heat source then supplies the optimum quantity of heat. An increase of the heat flow through the heat pipe, causing a rise of the temperature level, has no further favourable effect as regards reduction of the temperature differences between the heater pipes.

The invention will be described hereinafter with reference to the drawing which is a diagrammatic representation (not to scale) of an embodiment of the hotgas engine according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a plan view of a four-cylinder doubleacting hot-gas engine.

FIG. 2 is a sectional view along the line II-II of FIG.

DESCRIPTION OF THE PREFERRED EMBODIMENT The hot-gas engine of FIG. 1 comprises four cylinders 1, 2, 3 and 4, respectively, for four thermodynamic cycles. The regenerator and cooler which form part of a given cycle are each situated in a common space, i.e., in the spaces 5, 6, 7 and 8, respectively. The four cylinders as well as the spaces for regenerator and cooler are arranged in a ring. The space 7 of FIG. 2 accommodates a regenerator 9 and a cooler 10; the spaces 5, 6 and 8 are similar to space 7 and also contain a regenerator and a cooler which are not shown in the Figure,

In cylinder 3 is reciprocal piston 11, and situated above the piston is expansion space 12 to which heater pipes 13 are connected; the remote ends of these pipes extend into a duct 14. Arranged below piston 11 is compression space 15 to which a duct 16 is connected. Heater pipes 17 communicate with regenerator 9, the other end of these pipes opening into duct 14. A duct 18 communicates with cooler 10.

In a double-acting engine, the expansion space of one cylinder communicates with the compression space of a second cylinder via a heater, regenerator and cooler; the expansion space of the second cylinder communicates with the compression space of a third cylinder, again via a heater, regenerator and cooler.

In the present case, expansion space 12 in cylinder 3 is in open communication with the compression space inside cylinder 4 (not shown) via heater pipes 13, duct 14, heater pipes 17, regenerator 9, cooler 10 and duct 18. Compression space 15 inside cylinder 3 communicates with the expansion space inside cylinder 2 (not shown) via duct 16, the cooler and regenerator (not shown) inside space 6, and heater pipes (not shown).

The heater pipes associated with the four thermodynamic cycles are arranged in a ring about a space 20 for combustion gases. The hot combustion gases originate from one central burner device 21, having an inlet for combustion air 22 and an inlet for fuel 23. An outlet 24 for combustion gases communicates with space 20.

The upper parts of all heater pipes are arranged, together with the ducts which interconnect the heater pipes associated with one cylinder/regenerator combination (for example, duct 14 of FIG. 2) inside a common annular heat pipe 25, the inner wall of which is covered with a capillary structure 26. A small quantity of sodium is present in the heat pipe as a heat transport medium. The heat pipe furthermore comprises a heattransmitting wall 27 which is arranged in the flow path of the hot-combustion gases originating from burner device 21.

During operation of the hot-gas engine, the hot combustion gases flow along the heat-transmitting wall 27 and along the lower free heater pipe parts, while giving off heat thereto. Due to the taking up of heat from heat-transmitting wall 27, the sodium present in the heat pipe 25 evaporates. The sodium vapour flows to the heater pipe parts and their connection ducts due to the pressure prevailing at this area as a result of slightly lower local temperatures. This is because the working medium flowing through the heater pipes and their connection ducts takes up heat from the heater pipe walls and duct walls. The sodium vapour subsequently condenses on these walls while giving off heat thereto. Most vapour condenses at the areas where the lowest temperatures prevail. The temperatures of these walls are thus equalized. As a result, the upper heater pipe parts and their connection ducts are each isothermal and all have the same temperature. Consequently, the temperaturev of the working medium flowing through the heater pipes is equalized everywhere, with the result that working medium temperature differences between the pipes substantially disappear, which improves the power and the thermal efficiency of the engine. The surface of heat-transmitting wall 27 of heat pipe 25 is chosen to be so large that the heat flow to the heat pipe produces a sodium temperature which is substantially equal to the mean temperature of the lower pipe parts which are directly heated by the combustion gases. The quantity of heat taken up by the heat pipe is then optimum for achieving the desired temperature equalization. The thermal loading of the heat pipe is small which is desirable, because higher thermal loading does not improve the temperature equalization.

What is claimed is:

1. In a hot-gas engine including a burner providing a flow of hot combustion gases, an expansion space for working gas, and a heater using thermal energy from said combustion gases to heat said working gas, the heater formed of a plurality of pipes, each pipe having a first part thereof situated in the flow path of said combustion gases, the improvement in combination therewith comprising a heat pipe also situated in the flow path of said combustion gases, with a second part of each heater pipe situated inside the heat pipe, whereby said second parts of the heater pipes within the heat pipe are maintained at substantially the same temperature.

2. Apparatus according to claim I wherein said heat pipe has an annular shape, and said second parts of the heater pipes within the heat pipe are arranged to also define an annular shape. 7

3. Apparatus according to claim 1 wherein said heat pipe maintains the temperature of the heater pipe second parts therein at a temperature at least substantially equal to the mean temperature of the first parts of the said annular heat pipe and annular arrangement of heater pipes and engine axis all being coaxial.

5. Apparatus according to claim 4 wherein said heater pipes for the four cylinders form parts of a continuous conduit for said working gas, and said heat is a single component for providing thermal energy to all of said heater pipe second parts. 

1. In a hot-gas engine including a burner providing a flow of hot combustion gases, an expansion space for working gas, and a heater using thermal energy from said combustion gases to heat said working gas, the heater formed of a plurality of pipes, each pipe having a first part thereof situated in the flow path of said combustion gases, the improvement in combination therewith comprising a heat pipe also situated in the flow path of said combustion gases, with a second part of each heater pipe situated inside the heat pipe, whereby said second parts of the heater pipes within the heat pipe are maintained at substantially the same temperature.
 2. Apparatus according to claim 1 wherein said heat pipe has an annular shape, and said second parts of the heater pipes within the heat pipe are arranged to also define an annular shape.
 3. Apparatus according to claim 1 wherein said heat pipe maintains the temperature of the heater pipe second parts therein at a temperature at least substantially equal to the mean temperature of the first parts of the heater pipes outside the heat pipe which are directly heated by the combustion gases.
 4. Apparatus according to claim 2 wherein said engine has four working spaces situated annularly and in parallel about the engine axis, each comprising a compression and an expansion space, the compression space of each working space being in communication with the expansion space of another working space, said annular heat pipe and annular arrangement of heater pipes and engine axis all being coaxial.
 5. Apparatus according to claim 4 wherein said heater pipes for the four cylinders form parts of a continuous conduit for said working gas, and said heat is a single component for providing thermal energy to all of said heater pipe second parts. 